For the more studious:-)
Well, not that recent, but I am not sure if it's been presented here ... and has many valid points.
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http://www.biomech.com/db_area/archives/1999/9901function.51-60.bio-.html

BioMechanics
January 1999

Function Analysis:
New forehand options alter biomechanics of tennis

New rackets and grips mean more power and accuracy, but also the potential for increased injury.

By Rafael Bahamonde, PhD

ShooterMcMarco

09-29-2005, 03:21 PM

"The optimum angle of the racket in the vertical plane has been suggested to be 28º This angle provides good spin production and speed when the ball is struck properly. Smaller angles tend to produce less spin, while larger angles sacrifice ball speed and depth of the shot." in other words, nadal buggy whip vs. federer body wrap. "Regardless of the grip, stroke arc, swing, and footwork, proper execution of a topspin forehand stroke requires a nearly vertical or a slightly closed-face (slightly tilted forward) (7º) racket at impact" so this answers our questions about closed face: we have small margin for error if we try to hit it that way.